A jerkin is a man's short close-fitting jacket, made usually of light-coloured leather, and often without sleeves, worn over the doublet in the sixteenth and seventeenth centuries. The term is also applied to a similar sleeveless garment worn by the British Army in the 20th century.

What jerkin means?

: a close-fitting hip-length usually sleeveless jacket.

What is the difference between a jerkin and vest?

A jerkin is a highly structured article of clothing that follows the natural lines of the body. Most vests, on the other hand, are unstructured and loose-fitting. Jerkins are also traditionally worn over a long undergarment, such a doublet. Vests usually can be worn over any article of clothing.